Fluid Leak Diagnosis

This procedure systematically identifies the source of fluid leaks on the 2015-2020 Ford F-150 with 5.0L Coyote V8 engine using visual inspection, UV dye tracing, and component-specific testing.

Warnings

Tools required

Parts

• UV dye for engine oil × 1 — Use appropriate UV dye concentrate
• UV dye for coolant × 1 — Use appropriate UV dye concentrate
• UV dye for transmission fluid × 1 — Use appropriate UV dye concentrate

Preparation

1. Park vehicle on level surface and allow engine to cool completely
2. Chock rear wheels securely
3. Document any visible stains on driveway or garage floor with cardboard test
4. Gather UV dye kit and inspection tools
5. Have shop towels and degreaser ready for cleaning inspection areas

Procedure

1. 1

   Perform initial visual inspection from above
   Open hood and visually inspect engine bay for obvious fluid leaks. Check oil fill cap, dipstick tube, valve covers, oil filter housing, oil pressure sender, and front timing cover. Look for fresh fluid, wetness, or heavy accumulation of dirt indicating active leak points. Use flashlight to inspect difficult areas.
2. 2

   Inspect cooling system components
   Check radiator, radiator hoses, heater hoses, water pump (front of engine), thermostat housing (front driver side), coolant reservoir, and overflow hose connections. Orange coolant residue and white crusty deposits indicate coolant leaks. Inspect all hose clamps for tightness.
3. 3

   Check brake fluid and washer fluid systems
   Inspect brake master cylinder and brake lines at the master cylinder for DOT 4 LV brake fluid leaks (clear to light amber fluid). Check windshield washer reservoir for cracks or loose connections. These are typically blue fluid stains.
4. 4

   Raise vehicle for undercarriage inspection
   Raise front of vehicle with floor jack and support securely on jack stands at frame rails. Ensure vehicle is stable before going underneath. Lower jack slightly to confirm stands are supporting weight.
5. 5

   Inspect engine oil system from below
   From underneath, inspect oil pan gasket, oil drain plug area, oil filter, and oil cooler lines (if equipped). Check rear main seal area where engine meets transmission bellhousing. Look for fresh oil drips or heavy oil accumulation. The 5.0L Coyote commonly leaks from oil pan gasket and timing cover.
6. 6

   Inspect transmission and fluid cooler lines
   Check transmission pan gasket, transmission cooler lines running to radiator, transmission output seal, and dipstick tube (if equipped). MERCON LV ATF is red to dark brown. Follow cooler lines from transmission to radiator checking for leaks at connections and along line length.
7. 7

   Inspect rear differential
   Move to rear axle area and inspect differential cover gasket, pinion seal (front of differential where driveshaft connects), and axle seals at wheel hubs. Gear oil leaks appear as dark, thick oil with distinctive odor. Check for wetness and dirt accumulation.
8. 8

   Clean suspected leak areas
   Using brake cleaner and shop towels, thoroughly clean any areas where leaks are suspected. Remove all old fluid residue, dirt, and grime to create clean baseline for monitoring. This allows fresh leaks to be identified clearly during dye testing.
9. 9

   Add UV dye to appropriate systems
   Based on initial inspection findings, add appropriate UV dye to suspected leaking systems. Add oil dye through oil fill cap, coolant dye through reservoir, transmission dye through dipstick tube or fill plug. Follow dye manufacturer instructions for proper dosage. If leak source is unclear, dye all three systems.
10. 10

    Run engine and drive vehicle
    Start engine and allow to reach normal operating temperature (approximately 10 minutes). Drive vehicle for 20-30 miles under normal conditions to circulate dyed fluids through all systems and build operating pressures. This helps activate slow or intermittent leaks.
11. 11

    Perform UV dye inspection
    After drive cycle, raise vehicle again on jack stands. Using UV light in darkened area, inspect all previously cleaned areas. Dyed fluid will fluoresce brightly under UV light, making leak path clearly visible. Trace leak back to highest point of fluid travel to identify actual source, as fluid can run along components and drip from lowest point.
12. 12

    Verify and document findings
    Once leak source is positively identified, photograph the leak location with UV light for documentation. Wipe area with white paper towel under UV light to confirm fluid type by dye color. Note exact component and location for repair planning. Check that oil drain plug torque is correct if leak is from that area.
    Torque spec

    Oil Drain Plug35 Nm (26 lb-ft)

Reassembly

1. Lower vehicle from jack stands safely
2. Remove jack stands and lower jack completely
3. Clean UV dye from hands and tools before touching interior surfaces

Verification

• Leak source should be positively identified and documented with specific component location
• Fluid type should be confirmed by color, location, and UV dye response
• Leak path should be traced to highest point to ensure actual source is found, not just drip point
• Multiple leaks may be present - verify all fluid systems were properly inspected
• Plan appropriate repair procedure based on identified leak source

More procedures for this vehicle